The use of elastomeric materials in forming seals, e.g., annular ring seals and the like, is well known. It is generally thought useful to use elastomeric materials in such applications because of their inherently resilient nature that operates to provide a self-energizing force when loaded or squeezed into sealing position. This energizing feature operates to urge the seal into sealing contact against an adjacent surface to be sealed.
Elastomeric seals are used for many different applications. When installed in a rotary cone drill bit used for subterranean drilling operations, elastomeric seals are used to prevent grease that is used to lubricate a journal bearing within the bit from escaping. In such application it is desired that the elastomeric seal have a desired modulus of elasticity to provide a desired sealing force against an adjacent sealing surface when the seal is loaded or squeezed within the bit. In such applications, elastomeric seals have proven to be quite useful.
In such drill bit application, it is also necessary for the elastomeric seal to display properties other than and in addition to desired elasticity. Elastomeric seals used in drill bits are called on to provide sealing service in environments that are extremely harsh. Modern drill bits are being run at exceptionally high surface speeds, sometimes more than 500 feet per minute, with cone speeds averaging in the range of from 200 to 400 revolutions per minute. The life of an elastomeric seal in such application may be significantly degraded by high temperatures due to friction (as well as elevated temperature in the well bore) and abrasion. Additionally, such elastomeric seals can be degraded due to exposure with petrochemicals. Thus, in order to provide a consistently reliable elastomeric seal for maintaining the lubricant within the drill bit, it is desired that such seal displaying properties of heat resistance, wear resistance, and chemical resistance, in addition to desired resiliency.
However, the ability to provide an elastomeric seal having a desired level of all such properties is challenging, as these properties are interdependent on one another. Thus, when improved properties of hardness or wear resistance is desired, changing the elastomeric composition to achieve this goal can have a detrimental impact on the elastomeric resilience or modulus of the seal, i.e., increasing hardness or wear resistance will reduce elastomeric resilience or modulus. Because of this challenge, designers have explored different approaches to achieving desired combined properties.
One such approach known in the art involves constructing an elastomeric seal from two or more different elastomeric component, each specifically formulated to provide a certain desired performance property. One example of this approach comprises a annular seal comprising a seal body that is formed from one type of elastomeric material, e.g., one designed to provide a desired degree of resiliency, and a sealing surface along the seal body from another type of elastomeric material, e.g., formed from another type of elastomeric material designed to provide a desired degree of wear resistance or hardness. This type of elastomeric seal is one characterized by two distinctly different types of single-phase elastomers used to form different parts of the seal. While such elastomeric seals have provided some degree of improvement in achieving desired combined properties of resiliency and wear resistance over single elastomeric seals, such seals are still known to suffer from other performance issues common to single elastomeric seals.
A problem known to exist with conventional elastomeric seals is the unwanted build up of thermal energy, i.e., heat, during drill bit operation. This heat can be provided from the external operating environment of the drill bit itself, or by the friction of the elastomeric seal engaged within the bit. It is theorized that thermal energy is allowed to travel freely within such conventional elastomeric seals due to the continuous nature of the elastomeric structure. This is true regardless if the seal is constructed entirely from a single elastomeric material, or whether the sale comprises two or more different segments each constructed from a different elastomeric material.
In either case, such heat is known to build within such conventional elastomeric seals to the point where it can cause the seal to exhibit hysteresis, which causes the seal to lose desired properties of modulus, resiliency, tensile strength, and compression set. This is believed due to the fact that the elastomeric material undergoes vulcanization at the elevated temperature, causing the seal to harden, loose its resiliency, crack, and fail.
It is, therefore, desired that an elastomeric material be engineered in a manner that addresses the issue of unwanted heat build up when used in a sealing application. It is desired that such elastomeric material be constructed in a manner that addresses this issue without sacrificing desired properties of resiliency, wear resistance, chemical resistance, tensile strength, and compression set. It is further desired that such an elastomeric material permit the formation of seals, e.g., useful in drill bit applications, as a retrofit member, i.e., without having to modify the surrounding seal environment.